Effect of ageing process on bisphenol A sorption and retention in agricultural soils amended with biochar.

The ageing of biochar and organic pollutant itself in soils can both influence the retention of organic pollutant in field soils. In this study, column experiments were adopted to determine the effect of ageing process on bisphenol A (BPA) sorption and retention in two typical Chinese agricultural soils with lychee branch biochar added. The effect of biochar ageing on soil organic matter (SOM) was specially investigated. Experimental results showed that the addition of biochar significantly increased the condensation and rigid of SOM, which could further increase with biochar ageing in soils. As a result, the addition of biochar significantly increased BPA sorption capacity (5.86 times and 3.30 times) and retention rate (13.60 times and 4.47 times) in fluvo-aquic soil and phaeozem respectively, while BPA sorption capacity and retention rate decreased obviously after biochar ageing in the two soils for 2 months as compared with the freshly incorporated biochar treatments, which may be attributed to the surface coverage and/or pore blockage of some sorption sites owning to DOC. With biochar incorporated, 2 months of BPA ageing increased BPA retention rate by about 4.50 times in both soils as compared with BPA newly spiked treatments. The results of this study could provide important parameters for prediction and control of organic pollutants such as BPA in soils.

Fractionation and release of Cd, Cu, Pb, Mn, and Zn from historically contaminated river sediment in Southern China: Effect of time and pH.

The release of in situ heavy metals (cadmium [Cd], copper [Cu], lead [Pb], manganese [Mn], and zinc [Zn]) from contaminated river sediment near a Cu-iron mine in South China was experimentally studied. The effects of pH values and the kinetics of heavy metal release were investigated. In addition, species of the 5 metals in the sediment were determined as a function of pH and time. Rates and extents of metal desorption were studied over 30 d, and a 3-parameter, 2-compartment model was used to analyze the desorption kinetics. The rate constants (ks ) for the slowly desorbing fraction of heavy metals were found to be 5 to 6 orders of magnitude lower than the corresponding rate constants (kr ) for the rapidly desorbing fraction, suggesting that slow desorption is the rate-limiting step. The partition coefficients (Kd ) varied significantly among metals, on the order Pb > Cu >Zn > Cd > Mn, indicating that the sediment had a much higher retention capability for strongly hydrolyzed metals than for weakly hydrolyzed ones. The amount of metals released from the sediment decreased dramatically at the final pH of 2 to 4 and leveled off in the pH range of 5 to 8. Release time and pH exhibited a varied influence on the fractionation of metals, and had a more remarkable influence on more mobile fractions and hardly any effect on the residual fraction during the desorption process. The fractionation of strongly adsorbing metals like Pb was not as dependent on release time and pH as it was for the weakly bonded metals like Mn and Cd. The results indicate that in situ heavy metals may exhibit a sustainable potential for release and may increase health risks when the pH of the river is lowered. Environ Toxicol Chem 2019;38:464-473. © 2018 SETAC.

Enhanced reactivity of nZVI embedded into supermacroporous cryogels for highly efficient Cr(VI) and total Cr removal from aqueous solution.

Novel supermacroporous PSA-nZVI composites with nanoscale zero-valent iron particles (nZVI) embedded into poly (sodium acrylate) (PSA) cryogels were synthesized through ion exchange followed by in-situ reduction. The magnetic composites were evaluated for material characterizations and their efficiency for Cr(VI) and total Cr removal from aqueous medium in batch experiments. PSA-nZVI composites with high nZVI loading capacity up to 128.70 mg Fe/g PSA were obtained, and the interconnected macroporous structure of PSA cryogel remained unaltered with nZVI uniformly distributed on PSA cryogel as determined by TGA, SEM, TEM, XRD and XPS analyses. PSA-nZVI composites showed faster reaction rate than free nZVI both for Cr(VI) and total Cr removal, suggesting no mass transfer resistance and the enhanced reactivity of nZVI in PSA carrier. PSA-nZVI composites exhibited much more remarkable performance for Cr(VI) and total Cr removal than free nZVI particles in high removal capacity and broad pH application range (pH 4-10). The reaction mechanisms were also elucidated with XPS analyses before and after Cr(VI) reduction reactions. These results demonstrate that PSA cryogel acts as an excellent carrier and shows multiple functions in nZVI particle dispersion, pH buffering and oxidation resistance in addition to immobilizing nZVI particles from release.